Japanese Patent Application Laid-Open Publication No. 2003-114515 (Patent Document 1) describes a method for designing a mask. In the method, a region in which a dummy pattern can be disposed in a mask is determined on the basis of a mask pattern layout, and then, assuming that the dummy pattern is uniformly disposed in the whole region in which the dummy pattern can be disposed, a layout of the dummy pattern is determined so that values of parameters which are calculated in consideration of a dummy circuit pattern formed corresponding to the dummy pattern and a circuit pattern meet a standard.